The present invention pertains to a fixing fluid which, when applied over or under an inkjet ink, can enhance the properties of a printed image. The invention also pertains to an ink set comprising said fixing fluid and a printing method employing the ink set.
Inkjet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, to form the desired image. The droplets are ejected from a printhead in response to electrical signals generated by a microprocessor. Inks used in such recording are subject to rigorous demands including, for example, good dispersion stability, ejection stability, and good fixation to media.
Inkjet printers offer low cost, high quality printing and have become a popular alternative to other types of printers such as laser printers. However, inkjet printers are presently unable to match the speed of laser printers and the durability of the laser printed images. Inkjet prints with increased durability would be highly advantageous.
It is known in the inkjet art to print a fixer over and/or under a colored ink to enhance the coloristic and/or durability properties of the printed image. Typically, a fixer for dye inks is designed to increase water fastness, and a fixer for pigment inks is designed to increase chroma and/or optical density. However, fixers may also have other and/or additional beneficial effects.
Fixer fluids are generally also substantially colorless and do not perceptibly or substantially change the hue of a colored ink fixed by the fixer fluid. The fixing agents in the fixer are most commonly designed to operate by electrostatic interaction with a colorant. Thus, an ink with anionic dye or an anionic pigment dispersion is treated with a cationic fixing agent, or a cationic colorant is treated with anionic fixing agent, thereby immobilizing or “fixing” the colorant. This process is sometimes referred to in the art as “insolubilizing”, “precipitating” or “crashing” the colorant. Other mechanisms of fixation are also possible such as agents that immobilize colorant by sudden and dramatic pH or viscosity change. In some cases a combination of mechanisms may be operative.
It could be advantageous for a fixer to not only operate by an electrostatic mechanism but also covalently react and thereby provide even more durability. A covalent reaction can, for example, be crosslinking.
U.S. Pat. No. 5,693,127 discloses inks with alkoxysilane polyalkyleneimine adhesion promoters.
U.S. Pat. No. 6,180,690 discloses inks with alkoxysilane binder additives.
U.S. Pat. No. 6,461,419 discloses curable inks comprising compounds with two or three reactive silyl groups.
The disclosures of all of the above-identified publications are incorporated by reference herein for all purposes as if fully set forth.
There is still a need for inks and printing methods that provide more physically durable inkjet images.